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    <title>Apache Server Frequently Asked Questions</title>
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    <h1 align="CENTER">Apache Server Frequently Asked
    Questions</h1>

    <p>$Revision: 1.4 $ ($Date: 2001/10/08 01:26:54 $)</p>

    <p>The latest version of this FAQ is always available from the
    main Apache web site, at &lt;<a
    href="http://httpd.apache.org/docs/misc/FAQ.html"
    rel="Help"><samp>http://httpd.apache.org/docs/misc/FAQ.html</samp></a>&gt;.</p>
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    <p>If you are reading a text-only version of this FAQ, you may
    find numbers enclosed in brackets (such as "[12]"). These refer
    to the list of reference URLs to be found at the end of the
    document. These references do not appear, and are not needed,
    for the hypertext version.</p>

    <h2>The Questions</h2>

    <ol type="A">
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      <li value="8">
        <strong>URL Rewriting</strong> 

        <ol>
          <li><a href="#rewrite-more-config">Where can I find
          mod_rewrite rulesets which already solve particular
          URL-related problems?</a></li>

          <li><a href="#rewrite-article">Where can I find any
          published information about URL-manipulations and
          mod_rewrite?</a></li>

          <li><a href="#rewrite-complexity">Why is mod_rewrite so
          difficult to learn and seems so complicated?</a></li>

          <li><a href="#rewrite-dontwork">What can I do if my
          RewriteRules don't work as expected?</a></li>

          <li><a href="#rewrite-prefixdocroot">Why don't some of my
          URLs get prefixed with DocumentRoot when using
          mod_rewrite?</a></li>

          <li><a href="#rewrite-nocase">How can I make all my URLs
          case-insensitive with mod_rewrite?</a></li>

          <li><a href="#rewrite-virthost">Why are RewriteRules in
          my VirtualHost parts ignored?</a></li>

          <li><a href="#rewrite-envwhitespace">How can I use
          strings with whitespaces in RewriteRule's ENV
          flag?</a></li>
        </ol>
      </li>
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    </ol>
    <hr />

    <h2>The Answers</h2>
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    <h3>H. URL Rewriting</h3>

    <ol>
      <li>
        <a id="rewrite-more-config"
        name="rewrite-more-config"><strong>Where can I find
        mod_rewrite rulesets which already solve particular
        URL-related problems?</strong></a> 

        <p>There is a collection of practical solutions that can be
        found in the
        <a href="rewriteguide.html">Apache 1.3 URL Rewriting Guide</a>.
        If you have more interesting rulesets
        which solve particular problems not currently covered in
        this document, send it to <a
        href="mailto:rse@apache.org">Ralf S. Engelschall</a> for
        inclusion. The other webmasters will thank you for avoiding
        the reinvention of the wheel.</p>
        <hr />
      </li>

      <li>
        <a id="rewrite-article"
        name="rewrite-article"><strong>Where can I find any
        published information about URL-manipulations and
        mod_rewrite?</strong></a> 

        <p>There is an article from <a
        href="mailto:rse@apache.org">Ralf S. Engelschall</a> about
        URL-manipulations based on <a
        href="../mod/mod_rewrite.html"><samp>mod_rewrite</samp></a>
        in the "iX Multiuser Multitasking Magazin" issue #12/96.
        The German (original) version can be read online at &lt;<a
        href="http://www.heise.de/ix/artikel/1996/12/149/">http://www.heise.de/ix/artikel/1996/12/149/</a>&gt;,
        the English (translated) version can be found at &lt;<a
        href="http://www.heise.de/ix/artikel/E/1996/12/149/">http://www.heise.de/ix/artikel/E/1996/12/149/</a>&gt;.</p>
        <hr />
      </li>

      <li>
        <a id="rewrite-complexity"
        name="rewrite-complexity"><strong>Why is mod_rewrite so
        difficult to learn and seems so complicated?</strong></a> 

        <p>Hmmm... there are a lot of reasons. First, mod_rewrite
        itself is a powerful module which can help you in really
        <strong>all</strong> aspects of URL rewriting, so it can be
        no trivial module per definition. To accomplish its hard
        job it uses software leverage and makes use of a powerful
        regular expression library by Henry Spencer which is an
        integral part of Apache since its version 1.2. And regular
        expressions itself can be difficult to newbies, while
        providing the most flexible power to the advanced
        hacker.</p>

        <p>On the other hand mod_rewrite has to work inside the
        Apache API environment and needs to do some tricks to fit
        there. For instance the Apache API as of 1.x really was not
        designed for URL rewriting at the <tt>.htaccess</tt> level
        of processing. Or the problem of multiple rewrites in
        sequence, which is also not handled by the API per design.
        To provide this features mod_rewrite has to do some special
        (but API compliant!) handling which leads to difficult
        processing inside the Apache kernel. While the user usually
        doesn't see anything of this processing, it can be
        difficult to find problems when some of your RewriteRules
        seem not to work.</p>
        <hr />
      </li>

      <li>
        <a id="rewrite-dontwork"
        name="rewrite-dontwork"><strong>What can I do if my
        RewriteRules don't work as expected?</strong></a> 

        <p>Use "<samp>RewriteLog somefile</samp>" and
        "<samp>RewriteLogLevel 9</samp>" and have a precise look at
        the steps the rewriting engine performs. This is really the
        only one and best way to debug your rewriting
        configuration.</p>
        <hr />
      </li>

      <li>
        <a id="rewrite-prefixdocroot"
        name="rewrite-prefixdocroot"><strong>Why don't some of my
        URLs get prefixed with DocumentRoot when using
        mod_rewrite?</strong></a> 

        <p>If the rule starts with <samp>/somedir/...</samp> make
        sure that really no <samp>/somedir</samp> exists on the
        filesystem if you don't want to lead the URL to match this
        directory, <em>i.e.</em>, there must be no root directory
        named <samp>somedir</samp> on the filesystem. Because if
        there is such a directory, the URL will not get prefixed
        with DocumentRoot. This behavior looks ugly, but is really
        important for some other aspects of URL rewriting.</p>
        <hr />
      </li>

      <li>
        <a id="rewrite-nocase" name="rewrite-nocase"><strong>How
        can I make all my URLs case-insensitive with
        mod_rewrite?</strong></a> 

        <p>You can't! The reasons are: first, that, case
        translations for arbitrary length URLs cannot be done
        <em>via</em> regex patterns and corresponding
        substitutions. One needs a per-character pattern like the
        sed/Perl <samp>tr|..|..|</samp> feature. Second, just
        making URLs always upper or lower case does not solve the
        whole problem of case-INSENSITIVE URLs, because URLs
        actually have to be rewritten to the correct case-variant
        for the file residing on the filesystem in order to allow
        Apache to access the file. And the Unix filesystem is
        always case-SENSITIVE.</p>

        <p>But there is a module named <code><a
        href="../mod/mod_speling.html">mod_speling.c</a></code> in
        the Apache distribution. Try this module to help correct
        people who use mis-cased URLs.</p>
        <hr />
      </li>

      <li>
        <a id="rewrite-virthost"
        name="rewrite-virthost"><strong>Why are RewriteRules in my
        VirtualHost parts ignored?</strong></a> 

        <p>Because you have to enable the engine for every virtual
        host explicitly due to security concerns. Just add a
        "RewriteEngine on" to your virtual host configuration
        parts.</p>
        <hr />
      </li>

      <li>
        <a id="rewrite-envwhitespace"
        name="rewrite-envwhitespace"><strong>How can I use strings
        with whitespaces in RewriteRule's ENV flag?</strong></a> 

        <p>There is only one ugly solution: You have to surround
        the complete flag argument by quotation marks
        (<samp>"[E=...]"</samp>). Notice: The argument to quote
        here is not the argument to the E-flag, it is the argument
        of the Apache config file parser, <em>i.e.</em>, the third
        argument of the RewriteRule here. So you have to write
        <samp>"[E=any text with whitespaces]"</samp>.</p>
        <hr />
      </li>
    </ol>
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